@ Alpha84: I did have a couple of sessions (literaly) on a Naish Mutant, also 5'5", which has narrow nose and tail and wide in the middle, more rocker. Nothing special for riding and a bit unstable for jibing. Although didn't do much of jibing. Way too many fins.
I can say I started with Alaia totally green and immediately got the feel of it and instantly fell in love with it. Everyone who tries it (all green) might have some shaky knees starting the first run, crash at first transition, than they are already riping upwind the other way and also feel the love immediately. So I don't have any special talent here.
People actually like it so much, they started to ask me to bring the 2nd one, because they know I'm not very keen on switching with a TT (p.s.: I don't bring my TT lately, even if it's nuking).
I did try UD boards like skim, wave skim, kite fish after. Compared to my DIY Alaia they are all stiffer and don't perform/feel as good. Alaia is an absolute winner in upwind & downwind, smoothness/stability in chop (important for learning transitions) + speed, smoothness of carves without loosing speed and grip and not feeling fins draging. Wave skim is OK, but nothing special. Skim is to wide for my pref.
@BWD: I also prefer making it wider over making it longer to improve in low wind, however to certain extent, because you feel chop more and more, and i prefer smoother ride.
Since we are talking about Alaia, I think adding fins would make the greatest impact for bottom end performacne (I would also benefit from making a mixer test on my 19m2 S3, since I noticed increased downwind drag
If you can imagine, if you edge hard (to get the kite back up) you loose speed and at one point there is not enough board surface to keep you afloat and you instantly sink edge first. If you do not edge hard enough there is not enough water force to keep the board on the edge, so it flats-out and you get puled a bit downwind + loose some line tension.
Anyways, Alaia goes low enough, so I'm not realy considering any fins and the size suits me very well in 98%.